1. Field
The disclosure relates to a photoconductor and an image sensor including the photoconductor.
2. Description of the Related Art
A silicon-based complementary metal-oxide semiconductor (“CMOS”)/charge coupled device (“CCD”) image sensor technique has been mainstream in the related art for the past 20 years. By an optimized design and process, the CMOS/CCD image sensor technique has stably provided a pixel having a size of about 1 micrometer (μm), which is a diffraction limit of visible rays, and has high reliability as a technique for simultaneous integration with a logic device related to image processing. Particularly, the CMOS image sensor consumes a low amount of power, and may effectively be applied to almost all cameras of mobile devices. Each pixel of the CMOS image sensor includes a photodiode for absorbing light and converting the absorbed light to an electrical signal, and a logic device for processing the electrical signal. Recently, the photoelectric conversion device (e.g., a photodiode) has been downsized to about 1 μm, such that an amount of absorbed light is too decreased to enhance the image quality even if the pixel becomes smaller.
As alternatives of silicon conventionally used in a photodiode, an organic semiconductor and a quantum dot (“QD”) having higher light absorption by about 5-10 times that of silicon has recently drawn attention as a light absorber. In such an organic semiconductor and a QD, more light may be absorbed in a small area by having a high light adsorption rate. In addition, the organic semiconductor may provide a stacked structure because the organic semiconductor may selectively absorb light according to wavelength, thereby substantially improving the integration of an image sensor, and a colloid quantum dot has sensitivity that is comparable to the conventional monocrystal silicon with a thinner thickness by ten times that of silicon without an epitaxy process and has high compatibility with the silicon logic device.
The photo-detective structure using the colloid quantum dot operates in two ways, using a photodiode or a photoconductor. The photodiode has merits of a fast reaction speed and a low dark current even though the photodiode may not provide excited electron/hole pairs at greater than or equal to the number of absorbed photons. The photoconductor has drawbacks of a slow reaction speed and a high dark current, but the photoconductor may provide electron/hole pairs at more than several to ten times the number of the absorbed photons.